The invention relates to a method and an apparatus for grinding the exterior circumference of a rotating roller, held at its ends, with a rotating grinding wheel, whereby the length of the roller is a multiple of the width of the grinding wheel.
In many large-scale and industrial production processes, long narrow rollers are required that rotate during operation, sometimes must be driven, and often must be heated or cooled from inside. Such rollers can for instance have a length of approximately 1000 mm and a diameter of 85 mm. In addition the rollers are frequently tube-shaped with a low wall thickness that can be less than 1 mm. High stresses are placed on the surface quality of these rollers and on their dimensional stability. Grinding such rollers to final dimensions and the required surface quality therefore present great challenges to one skilled in the art.
One known disadvantageous aspect when grinding the exterior of rollers is that they bend outward laterally when the grinding wheel acts on their circumferential surface. This can lead to a situation in which the finished roller deviates from the cylindrical shape. In addition, the roller begins self-starting transverse vibrations, so-called regenerative chattering. The result of this regenerative chattering is chatter marks on the circumferential surface of the roller, which can cause reduced surface quality and thereby render the resultant roller unusable for many applications.
In order to prevent rollers from bending outward during grinding, it is known to support the roller at its exterior circumference with one or a plurality of steadies or rests. The steadies or rests comprise steel supports that support the blank. However, supporting the rotating roller on the steadies or rests comprising steel frequently leads to tracks, which can also cause reduced surface quality that cannot be tolerated. Known operating measures for eliminating regenerative chattering slow the grinding process.
One type of method mentioned in the foregoing known from commercial practice is that the roller is first rough-ground in the plunging method using a grinding wheel comprising corundum. For this, the roller is processed to a rough-ground dimension such that there are a plurality of successive plunges with the grinding wheel until the entire length of the roller has been rough-ground to this dimension. Subsequently this same grinding wheel is dressed and then fine- or finish-grinding is performed. Finish-grinding is done using longitudinal grinding, whereby the rotating grinding wheel and the rotating roller are moved relative to one another in the longitudinal direction of the roller on its exterior circumference. When the length of the roller is for instance 1,000 mm, grinding wheels with a width of for instance 100 mm are used. The disadvantage of this known method is that the grinding wheels comprising corundum must be dressed. This can even become necessary during a single finish-grinding process. Overall, the known grinding method is very tedious.
Known from DE 16 27 998 A1 is a follower rest for supporting cylindrical workpieces in a grinding machine that forms a hydrostatic semi-bearing. The rotating workpiece to be ground thus rests on a film of liquid that must be continuously replenished. An uninterrupted stream of liquid is fed to the hydrostatic semi-bearing for this purpose. The liquid can be a coolant that is always necessary when grinding. This known rest was used to achieve the goal of effectively supporting the workpiece, protecting its surface, and achieving a low-friction bearing, so that the rest does not need to be changed too often. Damping vibrations and avoiding chatter marks were not objectives with the known rests and therefore are also to a large extent unattainable with them. In addition, since the semi-bearing comprises metal, operation of the hydrostatic semi-bearing must be constantly and carefully monitored, because if the liquid film breaks down, then metal is on metal, which can damage the workpiece.
The object of the invention is therefore to create a method of the type cited in the foregoing that makes it possible to use CBN grinding wheels and that also enables substantially reduced processing times while still leading to rollers that have higher dimensional stability and surface quality.